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<pre><span class="comment"> /****************************************************************************
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 #include &lt;QtGui&gt;

 #include &quot;imageviewer.h&quot;

 ImageViewer::ImageViewer()
 {
     imageLabel = new QLabel;
     imageLabel-&gt;setBackgroundRole(QPalette::Base);
     imageLabel-&gt;setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
     imageLabel-&gt;setScaledContents(true);

     scrollArea = new QScrollArea;
     scrollArea-&gt;setBackgroundRole(QPalette::Dark);
     scrollArea-&gt;setWidget(imageLabel);
     setCentralWidget(scrollArea);

     createActions();
     createMenus();

     setWindowTitle(tr(&quot;Image Viewer&quot;));
     resize(500, 400);
 }

 void ImageViewer::open()
 {
     QString fileName = QFileDialog::getOpenFileName(this,
                                     tr(&quot;Open File&quot;), QDir::currentPath());
     if (!fileName.isEmpty()) {
         QImage image(fileName);
         if (image.isNull()) {
             QMessageBox::information(this, tr(&quot;Image Viewer&quot;),
                                      tr(&quot;Cannot load %1.&quot;).arg(fileName));
             return;
         }
         imageLabel-&gt;setPixmap(QPixmap::fromImage(image));
         scaleFactor = 1.0;

         printAct-&gt;setEnabled(true);
         fitToWindowAct-&gt;setEnabled(true);
         updateActions();

         if (!fitToWindowAct-&gt;isChecked())
             imageLabel-&gt;adjustSize();
     }
 }

 void ImageViewer::print()
 {
     Q_ASSERT(imageLabel-&gt;pixmap());
     QPrintDialog dialog(&amp;printer, this);
     if (dialog.exec()) {
         QPainter painter(&amp;printer);
         QRect rect = painter.viewport();
         QSize size = imageLabel-&gt;pixmap()-&gt;size();
         size.scale(rect.size(), Qt::KeepAspectRatio);
         painter.setViewport(rect.x(), rect.y(), size.width(), size.height());
         painter.setWindow(imageLabel-&gt;pixmap()-&gt;rect());
         painter.drawPixmap(0, 0, *imageLabel-&gt;pixmap());
     }
 }

 void ImageViewer::zoomIn()
 {
     scaleImage(1.25);
 }

 void ImageViewer::zoomOut()
 {
     scaleImage(0.8);
 }

 void ImageViewer::normalSize()
 {
     imageLabel-&gt;adjustSize();
     scaleFactor = 1.0;
 }

 void ImageViewer::fitToWindow()
 {
     bool fitToWindow = fitToWindowAct-&gt;isChecked();
     scrollArea-&gt;setWidgetResizable(fitToWindow);
     if (!fitToWindow) {
         normalSize();
     }
     updateActions();
 }

 void ImageViewer::about()
 {
     QMessageBox::about(this, tr(&quot;About Image Viewer&quot;),
             tr(&quot;&lt;p&gt;The &lt;b&gt;Image Viewer&lt;/b&gt; example shows how to combine QLabel &quot;
                &quot;and QScrollArea to display an image. QLabel is typically used &quot;
                &quot;for displaying a text, but it can also display an image. &quot;
                &quot;QScrollArea provides a scrolling view around another widget. &quot;
                &quot;If the child widget exceeds the size of the frame, QScrollArea &quot;
                &quot;automatically provides scroll bars. &lt;/p&gt;&lt;p&gt;The example &quot;
                &quot;demonstrates how QLabel's ability to scale its contents &quot;
                &quot;(QLabel::scaledContents), and QScrollArea's ability to &quot;
                &quot;automatically resize its contents &quot;
                &quot;(QScrollArea::widgetResizable), can be used to implement &quot;
                &quot;zooming and scaling features. &lt;/p&gt;&lt;p&gt;In addition the example &quot;
                &quot;shows how to use QPainter to print an image.&lt;/p&gt;&quot;));
 }

 void ImageViewer::createActions()
 {
     openAct = new QAction(tr(&quot;&amp;Open...&quot;), this);
     openAct-&gt;setShortcut(tr(&quot;Ctrl+O&quot;));
     connect(openAct, SIGNAL(triggered()), this, SLOT(open()));

     printAct = new QAction(tr(&quot;&amp;Print...&quot;), this);
     printAct-&gt;setShortcut(tr(&quot;Ctrl+P&quot;));
     printAct-&gt;setEnabled(false);
     connect(printAct, SIGNAL(triggered()), this, SLOT(print()));

     exitAct = new QAction(tr(&quot;E&amp;xit&quot;), this);
     exitAct-&gt;setShortcut(tr(&quot;Ctrl+Q&quot;));
     connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

     zoomInAct = new QAction(tr(&quot;Zoom &amp;In (25%)&quot;), this);
     zoomInAct-&gt;setShortcut(tr(&quot;Ctrl++&quot;));
     zoomInAct-&gt;setEnabled(false);
     connect(zoomInAct, SIGNAL(triggered()), this, SLOT(zoomIn()));

     zoomOutAct = new QAction(tr(&quot;Zoom &amp;Out (25%)&quot;), this);
     zoomOutAct-&gt;setShortcut(tr(&quot;Ctrl+-&quot;));
     zoomOutAct-&gt;setEnabled(false);
     connect(zoomOutAct, SIGNAL(triggered()), this, SLOT(zoomOut()));

     normalSizeAct = new QAction(tr(&quot;&amp;Normal Size&quot;), this);
     normalSizeAct-&gt;setShortcut(tr(&quot;Ctrl+S&quot;));
     normalSizeAct-&gt;setEnabled(false);
     connect(normalSizeAct, SIGNAL(triggered()), this, SLOT(normalSize()));

     fitToWindowAct = new QAction(tr(&quot;&amp;Fit to Window&quot;), this);
     fitToWindowAct-&gt;setEnabled(false);
     fitToWindowAct-&gt;setCheckable(true);
     fitToWindowAct-&gt;setShortcut(tr(&quot;Ctrl+F&quot;));
     connect(fitToWindowAct, SIGNAL(triggered()), this, SLOT(fitToWindow()));

     aboutAct = new QAction(tr(&quot;&amp;About&quot;), this);
     connect(aboutAct, SIGNAL(triggered()), this, SLOT(about()));

     aboutQtAct = new QAction(tr(&quot;About &amp;Qt&quot;), this);
     connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
 }

 void ImageViewer::createMenus()
 {
     fileMenu = new QMenu(tr(&quot;&amp;File&quot;), this);
     fileMenu-&gt;addAction(openAct);
     fileMenu-&gt;addAction(printAct);
     fileMenu-&gt;addSeparator();
     fileMenu-&gt;addAction(exitAct);

     viewMenu = new QMenu(tr(&quot;&amp;View&quot;), this);
     viewMenu-&gt;addAction(zoomInAct);
     viewMenu-&gt;addAction(zoomOutAct);
     viewMenu-&gt;addAction(normalSizeAct);
     viewMenu-&gt;addSeparator();
     viewMenu-&gt;addAction(fitToWindowAct);

     helpMenu = new QMenu(tr(&quot;&amp;Help&quot;), this);
     helpMenu-&gt;addAction(aboutAct);
     helpMenu-&gt;addAction(aboutQtAct);

     menuBar()-&gt;addMenu(fileMenu);
     menuBar()-&gt;addMenu(viewMenu);
     menuBar()-&gt;addMenu(helpMenu);
 }

 void ImageViewer::updateActions()
 {
     zoomInAct-&gt;setEnabled(!fitToWindowAct-&gt;isChecked());
     zoomOutAct-&gt;setEnabled(!fitToWindowAct-&gt;isChecked());
     normalSizeAct-&gt;setEnabled(!fitToWindowAct-&gt;isChecked());
 }

 void ImageViewer::scaleImage(double factor)
 {
     Q_ASSERT(imageLabel-&gt;pixmap());
     scaleFactor *= factor;
     imageLabel-&gt;resize(scaleFactor * imageLabel-&gt;pixmap()-&gt;size());

     adjustScrollBar(scrollArea-&gt;horizontalScrollBar(), factor);
     adjustScrollBar(scrollArea-&gt;verticalScrollBar(), factor);

     zoomInAct-&gt;setEnabled(scaleFactor &lt; 3.0);
     zoomOutAct-&gt;setEnabled(scaleFactor &gt; 0.333);
 }

 void ImageViewer::adjustScrollBar(QScrollBar *scrollBar, double factor)
 {
     scrollBar-&gt;setValue(int(factor * scrollBar-&gt;value()
                             + ((factor - 1) * scrollBar-&gt;pageStep()/2)));
 }</pre>
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